Internal combustion engines require distribution of lubricating oil to various components having hydraulic or lubricating requirements, such as bearings, bushings, tappets, camshaft phasers, lash adjusters, variable valve actuation devices, and hydraulic lifters. Engine lubricating oil typically resides in a sump and is pumped to the various components via an intricate system of oil galleries, from whence the oil is returned to the sump by gravity after use. Because the oil flow is split many times in satisfying the galleries, flow restrictions are known to be provided at various locations to cause various levels of backpressures and flow equalizations. These restrictions, which may be as small as 0.5 mm in diameter, or even smaller, are vulnerable to plugging by any contaminating particles carried by the oil which, once restricted or blocked, can present difficulty in purging air from the oil galleries.
Engine oil is dirtied in use by exhaust gas blowby from the cylinders and by frictional degradation, so a typical engine is provided with a global filtration system, either flow-through or bypass, that continuously filters oil during engine operation. Despite this filtration system, particulates are known to enter the oil galleries and foul the metering orifices. Hence, in a known Lifter Oil Manifold Assembly (LOMA), a regional filter is provided at the gallery entrance to the LOMA to screen out particulates from the lifter oil. Further, within the LOMA, up to four press-in-place metering valves are provided to act as flow limiters for gallery oil. These valves each contain a converging/diverging venturi orifice to create a homogeneous oil flow stream that constantly purges air from the control circuit (air is known to be drawn into the oil system under some engine operating and shutdown conditions).
In the prior art, the metering valves are formed of die-cast zinc and contain no filtration protection of their own. A two-stage manufacturing process is used to produce the valves in which the part is first cast and then the metering orifice is punched, or fabricated in some way, radially through the center of the valve. Manufacturing tolerances on the metering orifice as well as on the top plate that retains the valves in the LOMA are necessarily demanding, and therefore expensive to maintain, to prevent oil leakage around and retain the metering valves. Further, a shelf is cast into each of the supply channels of the top plate as a compression limiter to prevent the metering valve from creeping when assembled in place and during subsequent thermal cycling in the part application. Again, all tolerances are demanding. Further, the manufacturing process for the individual zinc-cast valves is relatively expensive.
What is needed in the art is an oil filtration assembly having an integral metering orifice downstream of the filter element, preferably wherein the assembly can replaceably substitute for a prior art cast metering valve.
It is a principal object of the present invention to improve reliability and ease of oil metering and air purging in a LOMA by providing immediate filtration protection of said valves.